Highly anisotropic helicene-based NLOphores for Two Photon Circular Dichroism (TPCD)
Lead Research Organisation:
University of East Anglia
Department Name: Chemistry
Abstract
Light comprises oscillating electric and magnetic fields (or alternatively a stream of photons ) propagating through materials. With modern laser techniques it is possible to generate intense irradiation that promotes multi-photon events such as second harmonic generation (SHG: frequency doubling). Visible light interacts with matter by exciting electrons from a low energy state (non-bonding or pi-bonding orbitals) to higher energy states (or virtual excited states in the case of SHG). Conventional dyes used in nonlinear optics combine donor (electron-rich) and acceptor (electron deficient) end-groups with an unsaturated linker. We will demonstrate that when the linker is twisted into a helix, the mirror image forms will allow novel experiments on two-photon circular dichroism (TPCD), an effect that although predicted has never been observed. The class of molecules chosen for study in this project have electrons in helical conjugated pi-systems, and this is the source of their handedness ( anisotropy / chirality ). A simple analogy to illustrate this is that my left-hand feels different if introduced into a right hand glove. The project seeks to define the differences when left-hand light or spin encounters right-handed or left-handed materials.To succeed, we need materials where the left- and right-hand forms are very different ( highly anisotropic ). With a large difference, there is the best prospect of characterising the consequences of the difference. Helices are fundamental left- and right-handed structures that occur in Nature in many ways. Their simplicity is a source both of great beauty and unique potential in scientific research. At a molecular scale, helicenes and heterohelicenes exhibit the same chiral properties (handedness). The choice of heterohelicenes for this project ensures highly anisotropic structures while retaining and extending the general form of the heterocyclic component of the linker in the well-established thiophene-linked ATOP and PETCN classes of NLO-responsive dyes. The approach to be adopted is the design and synthesis of novel helical analogues of ATOP and PETCN , by using tetrathiohelicenes in place of the simple thiophene ring of the conventional dye. This extension of the pi system will itself have a significant effect on the NLO properties, but crucially the helicenyl-linked derivatives have chirality built into the pi system. This will be evaluated as the basis for the discovery of the novel photophysics properties.The project will use new methods of kinetic resolution (KR) of helicenes, and employ multiple KR in the synthesis of the target molecules in exclusively left- or right-handed forms, by a method that exploits the different rates of reaction of the left/right-handed intermediates at several stages during the synthesis. We seek to compare two (D)-(chiral-pi)-(A) designs - (i) an unsymmetrical substitution pattern with a single (D)-(chiral-pi)-(A) feature spanning a full turn of the helix; (ii) a novel example with two shorter (D)-(chiral-p)-(A) structures each occupying a half turn of the helix.Collaborative strategies for experimental and theoretical evaluation of these molecular designs are proposed.
People |
ORCID iD |
G Richard Stephenson (Principal Investigator) |
Publications
Cauteruccio S
(2014)
A non-photochemical route to synthesize simple benzo[1,2-b:4,3-b']dithiophenes: FeCl 3 -mediated cyclization of dithienyl ethenes
in New J. Chem.
Doulcet J
(2015)
The Use of (-)-Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8-Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures.
in Chemistry (Weinheim an der Bergstrasse, Germany)
Doulcet J
(2015)
Novel Asymmetric Formylation of Aromatic Compounds: Enantioselective Synthesis of Formyl 7,8-Dipropyltetrathia[7]helicenes.
in Chemistry (Weinheim an der Bergstrasse, Germany)
Description | New examples of helical molecules with nonlinear optical properties New methods for the enantioselective synthesis of helicenes |
Exploitation Route | related designs using our double-dipole half-turn principle |
Sectors | Chemicals |
URL | https://www.uea.ac.uk/chemistry/people/profile/g-r-stephenson#researchTab |
Description | Our compounds are of interest to photophysics specialists because of the rarity of their helical pi systems |
First Year Of Impact | 2014 |
Sector | Chemicals |
Impact Types | Cultural |
Description | Interreg IVA AIcc |
Amount | € 988,444 (EUR) |
Organisation | European Commission |
Sector | Public |
Country | European Union (EU) |
Start | 11/2011 |
End | 06/2015 |
Title | design of helicenes for second harmonic generation |
Description | Additional SHG data from HyperRayleigh scattering (HRS), and CD data from circular dichroism spectra of enantiomerically pure tetrathiahelicenes witn powerful electron accepting groups at the ends of the helix has provided additional examples of the importance of our unconventional double-dipole half-turn design for helicene-based NLOphores. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2017 |
Provided To Others? | No |
Impact | Presently these results infulence the direction of my collaboration with the Verbeist group in Leuven. A joint paper is in preparation, and the double-dipole half-turn design will be the subject of a responsive mode EPSRC grant application. |
Description | Use of DFT calculations to preduct molecular structures and to assess nonlinear optical properties |
Organisation | University of Namur |
Country | Belgium |
Sector | Academic/University |
PI Contribution | This grant was itself to facilitate a collaboration with Claude Daul, but allowed me to create a new collaboration with Benoît Champagne |
Collaborator Contribution | Prof Daul made me a guest user on the High Performance Computing Facility at the University of Fribourg and I visited Fribourg to learn the to DFT calculations using Gaussian03, with guidance from him and his research group. The collaborations concerned the properties of helicenes, and Benoît Champagne at Namur had published an important paper in which he calculated that helicenyl structures should exhibit two photon circular dichroism (TPCD) a a level above the detection limit for direct observation. The collaboration with Champagne allowed me to visit Namur and work with his group, and I was given user access to the Belgium National high performance computational cluster through this collaboration. The nature of this computational work is such that I can launch Gaussian calculations for UEA to run remotely on either cluster, and similarly analyse the results. The travel in the collaboration is to learn how to do the science, and to discuss its outcomes. |
Impact | As a result of this collaboration I was able to buy a Gassian09 license for use on the "Grace" high performance cluster at UEA, and can teach my graduate students of to do DFT calculations, and to include the results in PhD theses, papers, and research proposals. There is a joint paper with Daul in the publications section of "outcomes". |
Start Year | 2007 |
Title | non-photochemical synthesis of benzodithiophene (BDT) regioisomer |
Description | BDTs are important components of solar cells, and commercially two particular regioisomers are used. Our work on helicenes requires an alternative regioisomer as a key starting point, and this is typically prepared by photolysis, which is not an easily-scalable procedure. We developed an alternative non-photochemical synthesis, and reported this IP to the University who approached industry and commissioned a report from experts, but in the end, no company expressed an interest and the decision was made not to patent the synthetic route but to wait for specific compounds and with properties advantageous in photocells and patent those. The University of Milan, however, did patent the alternative route developed by our collaborators (see collaborations section of outcomes), and the two academic groups shared information and published he two routes (see publications section of outcomes). |
IP Reference | |
Protection | Protection not required |
Year Protection Granted | |
Licensed | No |
Impact | Discussions drew attention to the fact that other isomers were available, but development costs were too high for them to challenge the established two isomers currently in wide-spread use. |
Description | Royal Society of Chemistry East Anglia Local Section Committee |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | Yes |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | A series of public events, and the hosting of RSC prize-winner lectures, are the main outcome of this activity (the whole committee contributes to this, not me as an individual). The most regular and successful event is a food-related scientific lecture/demonstration after the local section AGM, which is then followed by a dinner catered for by catering students at a local FE college, where the menu is themed to match the lecture. This is a "sell-out" every year (evidence of notable impact) and staff at the FE college have said that it sets an interesting challenge for their students, who also benefit from it. |
Year(s) Of Engagement Activity | Pre-2006 |
Description | Royal Society of Chemistry General Assembly |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | I was told afterwards by the Secretary that my comments had been valuable. Possible follow-up on best technologies for virtual meetings (e.g. teleconferencing) which I use at UEA within out EU Interreg project AI chem channel. |
Year(s) Of Engagement Activity | 2014 |
Description | School Visit |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | Talk on chemistry and the satisfaction gained from, and benefit to society from, careers in chemistry. The students asked lots of questions after the talk. The talk had employed audience response devices ("clickers") and the teacher present said that the children had liked the clickers and were pleased with the level of engagement. |
Year(s) Of Engagement Activity | 2014 |